"EnergyPlus" is a widely-used energy analysis and thermal load simulation program. Based on a user's description of a building from the perspective of the building's physical make-up, EnergyPlus calculates heating and cooling loads necessary to maintain thermal control setpoints.

"EnergyPlus" uses BSDF data as the optical representation of fenestration systems. The heat transfer through the system is solved based on the layer-by-layer model proposed at ISO15099.